Recently, various technologies for supporting an always-on function, in which IP communication is possible when a terminal is turned on, are being developed. Accordingly, it is expected that most high-end mobile terminals will support the always-on function within several years. When an always-on terminal is turned on, an IP address is allocated and therefore IP communication is possible. Thus, when data is received in a stand-by state after login to a service of a messenger, Voice over IP (VoIP), or IP Multimedia Subsystem (IMS), the messenger service, VoIP video communication, or e-mail reception is possible and also various services of a personal mini web server, and the like, are possible.
In a state in which the always-on terminal has logged in to a plurality of services, a plurality of TCP connections for maintaining communication connections to servers exist in an idle mode. A server for providing various types of services periodically sends a keep-alive packet to a mobile terminal so as to check a TCP connection to a counterpart mobile terminal. Then, the mobile terminal receives the keep-alive packet and sends an Acknowledgement (ACK) packet to the server in response thereto. The server receives the ACK packet from the terminal in response to the sent keep-alive packet, determines whether a communication connection between the server and the terminal is maintained, and continuously maintains the TCP connection.
Thereafter, the server is in the stand-by state until the next keep-alive packet is sent after newly setting a keep-alive timer as a timer for a stand-by time. When the keep-alive timer expires, the server checks the communication connection by re-sending the keep-alive packet to the terminal.
On the other hand, in the stand-by state, the terminal receives the keep-alive packet after changing the terminal state to a traffic state for receiving the keep-alive packet, and transmits an ACK packet to the server in response thereto. A change of the terminal state will be described with reference to the drawings.
FIG. 1 illustrates a current state variation when a conventional mobile terminal receives a keep-alive packet and sends an ACK packet. The mobile terminal receives the keep-alive packet and sends the ACK packet after a change from the stand-by state to the traffic state when the keep-alive packet is received in the stand-by state. After time T1, the mobile terminal returns to the stand-by state. After the server receives the ACK packet, a keep-alive timer corresponding to T2 is set. When the keep-alive timer expires after time T2, a communication connection is checked by re-sending the keep-alive packet to the terminal.
Time T1 is a value determined by a network policy of a provider as a time in which the terminal maintains a traffic state. When no data is transmitted and received during the time, the terminal returns to the stand-by state. For example, time T1 is set to approximately one minute in a Wideband Code Division Multiple Access (WCDMA) network of KTF established as Korea Telecom Freetel. In this case, since the terminal is in the traffic state during one minute for the reception of a keep-alive packet (about twenty bytes) and the transmission of an ACK packet (about twenty bytes), power is consumed.
A problem results from when one mobile terminal has a plurality of TCP connections to a plurality of servers. This will be described with reference to the drawings.
FIG. 2 illustrates an example in which a conventional mobile terminal 205 has TCP connections to a plurality of servers 210, 215, 220. The servers 210, 215, 220 are connected to one mobile terminal 205 over a communication network. Since each server 210, 215, 220 separately maintains a keep-alive timer, keep-alive packets whose number corresponds to the number of TCP connections to the servers 210, 215, 220 are scheduled and received by the mobile terminal 205.
FIG. 3 illustrates a current state variation of a conventional mobile terminal due to a keep-alive packet when the mobile terminal has TCP connections to a plurality of servers. When the mobile terminal is connected to four servers through four TCP connections, the duration of a traffic state for processing a keep-alive packet according to an operation by a keep-alive timer of each server increases even when a user does not use the mobile terminal. As the number of TCP connections increases, the duration of the traffic state is lengthened and therefore power consumption is increased.